The "copy an old campaign to skip this trap" idea is where I have to disagree. Copying a campaign copies all its settings too, and if the old one had display partners on, guess what you just carried over? I have seen people clone a winning campaign and inherit the same junk placements without knowing it. Building fresh takes 10 extra minutes and forces you to actually look at every box before you launch. The real fix is a launch checklist you run every single time, not hoping a copied campaign remembers to protect you.